[算法题] Add Two Numbers

题目内容

题目来源：LeetCode

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

题目思路

这个题目是倒序存储了两个数字，然后模拟进行加法运算。

本题中需要学习到的知识有：

1. 分别使用/和%来代表进位符号flag和当前位的值value

2. 成立哑结点（头结点），这样可以方便很多。

Python代码

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        if not l1 and not l2:
            return
        if not l1:
            return l2
        if not l2:
            return l1
        dummy=ListNode(-1)
        p=dummy
        flag=0
        while l1 and l2:
            value=(l1.val+l2.val+flag)%10
            p.next=ListNode(value)
            p=p.next
            flag=(l1.val+l2.val+flag)/10
            l1=l1.next
            l2=l2.next
        while l1:
            value=(l1.val+flag)%10
            p.next=ListNode(value)
            p=p.next
            flag=(l1.val+flag)/10
            l1=l1.next
        while l2:
            value=(l2.val+flag)%10
            p.next=ListNode(value)
            p=p.next
            flag=(l2.val+flag)/10
            l2=l2.next
        if flag>0:
            p.next=ListNode(flag)
        return dummy.next